The ivory barnacle, Balanus
eburneus, is a medium-sized sessile barnacle belonging to the
class Cirripedia. This group contains approximately 900 described
species, about two-thirds of which are free-living barnacles that
foul or attach to rocks and other hard intertidal and submerged
surfaces (Ruppert & Barnes 1994). Like other members of the
suborder Balanomorpha, the soft tissue of B. eburneus is
protected within a series of rigid plates, known as capitular plates.
The solid white plates of the ivory barnacle form a conical appearance
that is largest at the base, with a diamond-shaped opening guarded
by a movable opercular lid composed of two symmetrical triangular
halves (eg. Gosner 1978). Each of these halves contains
two plates, the tergum and the scutum. During feeding, excretion,
larval release and copulation, the operculum opens as the terga
and scuta are flexed out to the sides.
Potentially Misidentified Species
Several species of acorn
or balanoid barnacles inhabit the waters in and around the IRL.
Probably the most commonly confused species with B. eburneus
is the white bay barnacle, Balanus improvisus. This species
is usually smaller than B. eburneus, at a maximum height
of about 0.6 cm (Kaplan 1988). Definitive identification between
species of acorn barnacles similar in appearance usually requires
examination of the shape of the terga and scuta through dissection.
The striped acorn barnacle, Balanus
amphitrite, is similar in size and shape, but bears pink
vertical stripes on the capitular plates. The non-native titan acorn
barnacle, Megabalanus coccopoma,
recently discovered in Florida waters as of the date of this text,
has plates that are distinctly pink in color. The average size of
most M. coccopoma is considerably larger than the other
acorn barnacles found in Florida.
HABITAT AND DISTRIBUTION
Regional Occurrence & Habitat Preference
The range of the ivory
barnacle is extensive, probably due in part to introductions of
the species via the ballast water and hull fouling of ships (eg.
Hawaii, Matsui et al. 1964). The native distribution of
B. eburneus extends from Nova Scotia to Florida, the Caribbean
and Gulf of Mexico (Kaplan 1988). Large aggregations of the barnacle
can be found on a variety of hard surfaces at or below the low tide
line to a depth of about 37 m (Voss 1980), including: rocks; oysters,
mussels and other mollusk shells; pilings; buoys; seawalls and prop
roots of the red mangrove, Rhizophora
mangle (Kaplan 1988, Ruppert & Fox 1988, Voss 1980,
The ivory barnacle is considered
one of the most common fouling organisms found in the IRL (Hoskin
& Courtney 1983, Mook 1976). Single individuals to large aggregations
can be found in all intertidal IRL habitats.
LIFE HISTORY AND POPULATION BIOLOGY
Age, Size and Lifespan
The maximum age of B. eburneus is unknown, and the
lifespan can vary with food availability and environmental factors.
The maximum reported height and diameter for the ivory barnacle
is about 2.5 cm (Gosner 1978, Kaplan 1988), though most specimens
are much smaller.
The ivory barnacle is gregarious like many
other balanoid species (Toonen 2005). Occasional solitary individuals
can be found on mangrove roots or pilings, but most larvae settle
near others to produce large aggregations of several thousand individuals,
covering the substrate and often growing on top of one another.
Like most other free-living barnacles, B.
eburneus is hermaphroditic. However, populations reproduce
via cross-fertilization. The penis of B. eburneus is quite
long, and can be protruded out of the body and into the mantle cavity
of nearby individuals where sperm is deposited on the first cirri
of the recipient before penetrating the ovisac and reaching the
lamellae or egg mass (Ruppert & Barnes 1994). The eggs are brooded
in the mantle cavity and released as swimming larvae once development
Once they are released from the parent, larvae
of B. eburneus pass through six naupliar stages and one
cypris stage (Costlow & Bookhout 1957). The first nauplius is
a non-feeding stage, but larvae in the following five developmental
stages feed on phytoplankton. The non-feeding cyprid is the final
larval stage, subsisting on lipid (fat) reserves accrued through
naupliar feeding. The primary goal of this stage is to find suitable
habitat on which to settle and metamorphose into a juvenile barnacle,
usually after a total planktonic duration of 7-13 days (Costlow
& Bookhout 1957). Several cues such as the presence of other
B. eburneus, and the texture and biofilm (slime layer)
composition of the substrate can influence cyprid settlement (eg.
Dineen & Hines 1994, O'Connor & Richardson 1994). Once an
appropriate site has been found, cyprids attach to the substrate
as they are metamorphosing by secreting an adhesive substance from
cement glands at the base of the 1st antennae (Ruppert & Barnes
Based on the range and distribution of
B. eburneus throughout temperate to tropical latitudes,
the thermal tolerance of the ivory barnacle is likely quite large.
The ivory barnacle is a euryhaline species,
capable of withstanding a wide range of salinities. Large populations
are commonly found in the field in waters from 5-30 ppt (Bacon 1971).
In the laboratory, cypris larvae of B. eburneus settled
at salinities ranging from 2 to 35 ppt, although the highest settlement
occurred between 15 and 20 ppt (Dineen & Hines 1994).
Barnacles are filter feeders, extending
their long feeding appendages (cirri) to remove zooplankton and
microalgae from the water column. During feeding, the paired scuta
and terga open and six pairs of cirri unroll and extend through
the aperture (Ruppert & Barnes 1994). Long setae, or hair-like
projections, cover the cirri to form a basket-shaped netting apparatus
which strokes through the water to collect plankton.
Few predators are recorded for B. eburneus,
but individuals are likely preyed upon by a variety of fishes and
No known obligate associations exist for B.
eburneus. However, ivory barnacles are associated with several
organisms common to intertidal areas. For extensive lists of other
species found in the habitats in which B. eburneus occurs,
please refer to the "Habitats of the IRL" link at the left of this
Economic & Ecological Importance
other species of barnacles, B. eburneus poses an economic
threat to several marine-associated industries. Adults and juveniles
can attach to ship hulls, creating drag and increasing fuel costs.
In addition, intakes of marine-cooled nuclear power plants can become
fouled, requiring costly removal. In regions where the ivory barnacle
is invasive, B. eburneus can alter food webs and have other
devastating impacts on local ecosystems. However, in their native
habitat, ivory barnacles and their associated fouling organisms
can form extensive fouling communities that provide a home and food
source for a variety of coastal fishes and invertebrates.
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